Brain ultrasound

概述

Brain ultrasound — sometimes called cranial ultrasound, head ultrasound, brain sonography or neurosonography — uses sound waves to make pictures of the brain.

Brain ultrasound is most often used in newborns and infants because the soft spots between skull bones, called fontanels, let sound waves reach the brain. The procedure can help look for bleeding, fluid buildup, enlarged spaces in the brain or other changes.

During pregnancy, fetal ultrasound or another ultrasound test called fetal neurosonography can check the developing brain before birth. In older children and adults, brain ultrasound usually is not used to make routine brain pictures because the skull blocks sound waves. However, ultrasound may be used in other ways, such as to check blood flow to the brain, guide some brain surgeries or treat some conditions.

Most brain ultrasound uses a device outside the body. Ultrasound done during pregnancy may involve placing a small device inside the body.

Types

Brain ultrasound may refer to several tests and procedures.

• Fetal ultrasound. This type of routine ultrasound is used to look at the anatomy of an unborn baby, also called a fetus. This may include looking at the developing brain. A type of fetal brain ultrasound that offers a more detailed look at the brain is called fetal neurosonography. These tests can help diagnose or monitor certain conditions before birth.

• Head ultrasound. This type of ultrasound is used to create pictures of the brain in newborns and infants. It can help diagnose and monitor some conditions. Head ultrasound can be used in babies because the soft spots between skull bones, called fontanels, allow sound waves to reach the brain. These soft spots usually close as a child grows. Other names for head ultrasound in babies are cranial ultrasound, cranial sonography, neonatal brain ultrasound or neurosonography.

  In older children and adults, brain ultrasound usually is not used to make routine brain pictures because the skull blocks sound waves.

• Transcranial Doppler ultrasound. This type of ultrasound may be used to check blood flow in brain blood vessels as part of diagnosing or monitoring some conditions.
• Intraoperative brain ultrasound. Brain ultrasound sometimes is used during brain surgery to help guide the surgery.
• Focused ultrasound. Focused ultrasound uses targeted ultrasound energy as a treatment for some brain conditions. It is different from ultrasound tests used to create pictures or check blood flow.

目的

A healthcare professional may order brain ultrasound for several reasons.

Help diagnose or monitor conditions

Fetal ultrasound is a routine test done during pregnancy. A more detailed test called fetal neurosonography can be used when a routine fetal ultrasound suggests a possible brain difference or when a care team needs a closer look at the brain. Both types of ultrasound may be used to check for brain damage, brain conditions or other changes, such as:

• Brain bleeds or other blood flow issues.
• Bigger than usual head size or bigger than usual fluid spaces in the brain, called ventricles. This finding may suggest conditions such as hydrocephalus.
• Smaller than usual head size, a condition called microcephaly. In babies, this condition can have a number of causes. Examples include infections during pregnancy, such as Zika virus and cytomegalovirus, gene changes such as those that cause Down syndrome, and craniosynostosis.
• Differences in how the brain or skull is forming.

Head ultrasound in newborns and infants, sometimes called cranial ultrasound, neonatal brain ultrasound, cranial sonography and neurosonography, may be done to look for or find conditions such as:

• Possible bleeding in the brain, for example intraventricular hemorrhage. Premature birth can increase the risk of bleeding or injury in the brain.
• Larger than usual fluid spaces in the brain, called ventricles, which may be caused by bleeding and lead to hydrocephalus or other conditions.
• Injury in the white matter of the brain. This can be linked to conditions that affect movement or development, such as cerebral palsy.
• Seizures, fast head growth or other signs of a brain or nervous system condition.
• Craniosynostosis.

A head ultrasound might be done in an infant to confirm a brain finding seen before birth or on an earlier test. Some infants born early also may have this test.

A typical brain ultrasound in a newborn does not show signs of bleeding, extra fluid buildup or major differences in how the brain formed.

Transcranial Doppler ultrasound may be done in children and adults to look at how blood moves through blood vessels. This can help check for:

• Stroke risk in children with sickle cell disease.
• Narrowed or blocked blood vessels to or in the brain, commonly caused by atherosclerosis.
• Tiny clots called emboli moving through blood vessels in the brain.
• Blood vessel spasms after a brain bleed.
• Blood vessel response to stress.
• Blood flow changes that may suggest heart conditions.

Help guide surgery

Ultrasound may be used during some brain surgeries. For example, it may be used in some skull base surgeries, such as those for vestibular schwannomas and, possibly, pituitary tumors.

During brain surgery, ultrasound may help:

• Find a known brain tumor.
• Show nearby brain structures in real time.
• Check how much tumor has been removed during surgery.
• Adjust for changes in the brain during surgery.
• Support other tools, such as MRI.

Help as a treatment

High-intensity focused ultrasound may be used to treat some people with:

• Essential tremor.
• Parkinson's disease.

When used to treat these conditions, focused ultrasound is less invasive. It may improve tremor by using heat from the ultrasound to destroy a tiny, targeted area of brain tissue involved in tremor.

Focused ultrasound is different from deep brain stimulation, which involves implanting electrodes in the brain to send electrical impulses that can affect brain activity. Deep brain stimulation is an invasive procedure but can be adjusted over time. With this type of focused ultrasound, changes to the brain are lasting.

Focused ultrasound also is being studied as a possible way to open the blood-brain barrier for a short time. This may help medicines reach the brain to treat conditions such as Alzheimer's disease. Researchers also are studying lower energy focused ultrasound as a way to affect activity in certain areas of the brain without destroying or heating brain tissue. This is sometimes called ultrasound brain stimulation or neuromodulation.

风险

The risks of brain ultrasound depend on how it's used.

When used to help diagnose or monitor conditions

Fetal ultrasound during pregnancy is considered safe. It uses low-power sound waves, and there are no known risks.

Head ultrasound and transcranial Doppler ultrasound also are considered safe. There are no known risks.

When used to guide surgery

The main risks of ultrasound used during brain surgery are usually related to the surgery itself, not the ultrasound.

When used as a treatment

Focused ultrasound treatment has more risks than other uses for brain ultrasound. Some side effects may last or not go away. Some are mild or go away on their own.

When focused ultrasound is used to treat essential tremor and Parkinson's disease, possible side effects include:

• Headache or nausea.
• Trouble swallowing.
• Tingling or numbness.
• Trouble with balance or walking that is not steady.

Focused ultrasound also is being studied as a possible treatment for other brain and nervous system conditions. These uses and the risks of each are still being researched.

如何进行准备

To prepare for any ultrasound, you might be asked to:

• Wear loose clothing to your appointment.
• Leave valuables, such as jewelry, at home.

Depending on the reason for the brain ultrasound, you may be asked to do some other things to prepare.

When used to diagnose and monitor conditions

For some fetal ultrasounds, your healthcare team may ask you to:

• Drink a certain amount of water shortly before the exam to make sure your bladder is full.
• Avoid emptying your bladder until after the exam.

For head ultrasounds in a baby or transcranial Doppler ultrasounds in a child or an adult, special preparation usually is not needed. Adults who use products with nicotine may be asked to stop for a short time before the exam. This is because nicotine may narrow blood vessels. Your healthcare team can tell you whether there are any specific steps you need to take to prepare.

When used to guide surgery

The care team usually gives surgery preparation instructions if ultrasound is used during brain surgery. The instructions may include what to do about things such as food, drink and medicines ahead of the procedure.

When used as a treatment

The care team usually gives preparation instructions for focused ultrasound treatment. This may include what to do about things such as food, drink and medicines ahead of the procedure.

Before the procedure, you also may need:

• An MRI or other imaging to find the target area and plan treatment.
• Tests to check your coordination.

What you can expect

What happens during and after brain ultrasound depends on how the ultrasound is used.

Before the test or procedure

Before brain ultrasound, you may be asked to:

• Remove jewelry.
• Change into a gown.

During the test or procedure

What to expect during brain ultrasound depends on the reason for the procedure and the type used.

• When used to diagnose or monitor conditions. During a fetal ultrasound, you usually lie on an exam table. Warm gel is applied to the skin. The gel helps prevent air pockets, which can block the sound waves that create the ultrasound images. The gel is water-based and easy to remove from skin and, if needed, clothing.

  A trained technician called a sonographer uses a small, hand-held device called a transducer. The technician presses the transducer against your body and moves it as needed to capture the images. The transducer sends sound waves into your body and collects the sound waves that bounce back. The images then appear on a computer screen.

  You also may have a vaginal ultrasound. For this, the technician places a special transducer in your vagina.

  Fetal ultrasound usually is painless. But you may feel mild discomfort during a vaginal ultrasound. The technician doing the ultrasound may ask you to change positions during the exam to get clearer pictures. The exam usually takes 30 to 60 minutes.

  For a head ultrasound in a baby, the ultrasound is done with a transducer placed on the baby's head, usually over a soft spot called a fontanel. Gel is used to help make the pictures.

  For a transcranial Doppler ultrasound exam in a child or an adult, you may be seated or reclined. The transducer may be placed on different areas of the head and neck. These may include the temples, areas near the ears, closed eyelids and back of the neck.

  Most ultrasound exams are painless. If you're having a transcranial Doppler ultrasound, you also may hear sounds of the blood flowing through the blood vessels or pulselike sounds that change in pitch. The exam may take 30 to 90 minutes.

• When used to guide surgery. When ultrasound is used during brain surgery, it happens during the operation. Surgeons use a portable intraoperative ultrasonography machine to make real-time images of the brain. For example, these images can help the surgeon find a known tumor, see nearby brain structures or check how much of a tumor has been removed. The images also may help a surgeon adjust for shifts in the brain that happen during surgery.
• When used as a treatment. For focused ultrasound used to treat essential tremor or Parkinson's disease symptoms, you may wear a special head frame. The head frame helps hold the head in place and connects it to the ultrasound transducer that focuses many ultrasound beams on a specific area in the brain. The high-intensity ultrasound waves create heat that destroys a small area of tissue. The surgeon also may use MRI to target the correct area of the brain and be sure the sound waves are creating the exact amount of heat needed for the procedure. You generally are awake during the procedure so your care team can check for symptoms or changes in movement or coordination.

After the test or procedure

What happens after brain ultrasound may be different depending on why you had the ultrasound and the type used.

• When used to diagnose or monitor conditions. After a fetal ultrasound, you usually can go back to your regular activities right away. Ask your healthcare team when to expect results. After a head ultrasound in a baby or a transcranial Doppler ultrasound in a child or an adult, the technician removes any gel from your skin. You may be asked to wait in case more imaging is needed. You usually can return to your typical activities right away.
• When used to guide surgery. After brain surgery that uses ultrasound, your recovery depends on the type of surgery, not the ultrasound itself. Ask your surgical team what to expect after surgery.
• When used as a treatment. After focused ultrasound treatment, your care team monitors you. You may have an MRI to check the treated area. Most people go home the same day. Depending on the procedure, you may need someone to drive you home. Ask your care team when you can return to your usual activities.

结果

Results depend on how brain ultrasound was used.

When used to diagnose or monitor conditions

After a fetal ultrasound, your healthcare team explains what the images show. It can be stressful to hear that a fetal ultrasound shows a possible brain or head difference. But a possible difference does not always mean that a baby has a serious condition. The care team may need a closer look with a more detailed ultrasound or fetal MRI. These tests may help the care team plan follow-up and care after birth. Sometimes the care team might suggest genetic counseling to help explain what the finding could mean for your baby.

After a head ultrasound or transcranial Doppler ultrasound, a radiologist or another trained healthcare professional reviews the images. That person sends a report to your healthcare team. Your care team then explains the results to you.

Your next steps depend on what the ultrasound shows and why it was done. Your healthcare team may recommend follow-up exams, another imaging test or treatment for the condition found.

When used to guide surgery

After surgery, your care team explains what was found and what follow-up is needed.

When used as a treatment

Results of treatment vary depending on the reason for treatment, the seriousness of the condition, your overall health and other factors. Your healthcare team can tell you what outcomes are possible for your situation.